Television system



March 15, 1938. R. CAMPBELL TELEVISION SYSTEM Original Filed June 1, 1953 2 Sheets-Sheet l Tf* IL MRR n1. 58km. Om+ uw.

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AL S 5, 1938- R. L. CAMPBELL.

TELEVISION SYSTEM original Filed June 1, 1953 2 sheets-snee*u 2 WER.

Patented Mar. 15, 1938 UNITED STATES PATENT OFFICEl TELEVISION SYSTEM Application June 1, 1933, Serial No. 673,833 Renewed August 6, 1937 14 Claims.

My invention relates to improvements in television systems. In a television transmission system of one type, the picture signals are developed by apparatus in the form of a cathode ray tube comprising a mosaic photosensitive screen onto which an image of the object is projected, and an electron gun which develops a ray of electrons and drects the same at the screen. In operation, the ray is caused to scan the screenI by electromagnetic coilsor by plates. When coils are used, a saw-tooth current wave at a relatively high frequency is caused to pass through one set of` coils signals are developed electrically, and transmitted in the same electrical channel, as in the. system disclosed in my copending application bearing Serial No. 672,963, filed May 26, 1933, and assign-ed to Radio Corporation of America, occurrence of each framing signal is accompanied by the occurrence of several synchronizing signals.

These signals add together in the common amplilier therefor to develop a given Wave shape, which might vary from one frame to the next. If this action occurs, the possible effect is that the receiving apparatus falls out of frame. Y

Another possible disadvantage in the various systems proposed heretofore resides in the fact that the effectiveness of the horizontal synchronizing signals is interrupted during occurrence of the framing signals of greater duration. The result of this action is that during each frame the receiving apparatus is deprived of several synchronizing signals, and under certain conditions falls out of synchronism before the synchronizing signals again appear. mind, the object of my invention is to provide an improved television transmission system which avoids the difficulties and disadvantages referred to.

More particularly, an obect of my invention is the provision of an improved television transmission system wherein synchronizing Signals Withl all the. foregoing in l and framing signals are transmitted in the same electrical channel under conditions which prevent the simultaneous occurrence. of the synchronizing and framing signals in the common amplifier therefonand, further, wherein the horizontal 5 synchronizing signals are transmitted continuously for constant use at the receiver, without interruption by occurrence of framing signals, as heretofore.

Other objects and advantages will hereinafter appear.

In accordance with my invention, the. synchroynizing and framing signals are developed in separate `circuits which supply .ai common electrical channel in which both kinds of signals appear and are amplified for transmission. In one embodiment of my. invention, the framing signals are taken@ from the circuit developing the same and are applied to the other circuit and are utilized therein to prevent occurrence of the synchronizing signals simultaneously with the framing signals in the common amplifying channel. In another embodiment of my invention, the synchronizing signals are applied to the circuit for developing the framing signals and are utilized therein to suppress or interrupt each framing signal for a period of time somewhat greater than the period of duration of each synchronizing signal. ThisA action, when represented graphically, results in the formation of gaps in the framing signals. The synchronizing signals, which would otherwise be lost during occurrence of the framing signals, then appear effectively in these gaps, so-called, so that there is no interruption in the transmission of the synchronizing signals. The suppression or interruption of the framing signals, in the manner and for the purpose explained, is not such as to render the framing signals ineffective for satisfactory framing action at the receiving apparatus.

My invention resides in the improved system, apparatus and method of the character hereinafter described and claimed.

For the purpose of illustrating my invention, an embodiment thereof is shown in the drawings, wherein Figure l is a diagrammatic view of a television transmission system embodying and operating in accordance with my invention;

Figs. 2, 2a, 3 and 3a areschematic views, il- 50 lustrative of the operating action of the system shown in Fig. l;

Fig. 4 is a view similar to Fig. modification; and

Figs, 5 and 6 are schematic views, illustrative 55 1, showing a of the operating action of the system shown in Fig. 4. Y

The reference numeral Ill designates a cathode ray tube for developing picture signals. This tube comprises suitable photosensitive, mosaic screen structure I2, which, for example, may be made up of a great number of minute, photosensitized silver globules supported on a metallic base plate and each insulated from the latter and from each other. A suitable electron gun I4 operates to develop a ray I6 of electrons and to'direct the same at the screen structure. `4The tube is provided with a grounded anode in the form of a silver coating I'I on the inside surface.

The ray I6 is caused to scan a rectangular area or frame of the screen structure forty-eight times a second. During relatively short periods between the frames, the ray is returnedto the initial starting point for the nextv succeeding frame.

. Let it beassurned; for example, that there are to be-'48 pictures or framesa second. 'Forthese conditions, the rayis deflected horizontally by two coilsI8 throughlwhich 'a saw-tooth current Wave is". caused topass at a frequency.A of 5832 cycles. A suitable-generator supplies the current wave for this purpose. Also, the ray is deected .verticallybytwo coils 22 through which a saw-tooth current wave is causedtopass at a frequency of '4S-cycles. VvA suitable generator 24 supplies the current wave for this purpose.

'Ihe'electron gun l4-isiprovided with acontrol electrode or grid 2B Vbly-which the intensity of the ray is `varied in the manner and for the purpose hereinafter explained.

An image of the object 28, which may be an *outdoor View, astudioV scene, or a moving-picture film, is projected onto the screen .I2 by a suitable lens system 130.

Looking-toward `the `right in the drawings, as

the ray I6 scans the screen from left to right,

`individual electrostatic charges, previously stored `on the globules'constituting the surface of the there will be A1171/2 picture lines-for each frame.

Under such conditions, for every 48 frames the ray I6 will be cause-d to scan vthe 24 odd frames along the same,lspaced, parallel lines, and to lscan the24 even frame-salong the same parallel lines' between 'thefirst-mentioned lines.

This method of scanning is referred to as interlaced scanning, and vis disclosed in detail in the copending application by Randall C.`Ballard, bearing Serial No. 623,325, Yfiled-July 19, 1932,and

assigned to the Radio Corporation of America.

My invention is particularly useful in systems employing interlaced scanning, for the reason hereinafter explained.

f For' the purpose of maintaining operating action of the generators 20 and 24 at the respective frequenciesf a suitable generator 46 is utilized to develop-controlsignals which occur at the rate of 5832 a second, and other control signalswhich occur at 'the rate of 48 a second. The relative amplitude of these control signals and theirioccurrencewith respect to the time from these'coils to the grid of the tube 50.

axis is indicated at 48 and 5I), respectively, from which it Will be noted that the control signals for vertical deflection are o-f much longer duration than the control signals for horizontal deflection, and that both of these signals are of the same amplitude. To avoid prolixity, the signals first referred to will, hereinafter, be designate-d asl horizontal-control signals, andA the second mentioned signals as vertical-control signals.

The generator 46 may, though not necessarily, be in the form of an apertured disc of the general type disclosed in the copending application by Arthur W. Vance, Serial No. 544,959, led July k17, 1931,' and assigned to Radio Corporation of America. )The apertures in the disc (not shown) are such that the control signals have the same amplitude, the vertical-control signals, however, Abeing of greater duration than the horizontalcontrol signals and occupying a time period equal to four horizontal return-line periods. After amplification in an amplier 52,thecontrol .sig-

nals are impressed across resistors` 54. and 56. and

applied therefronrito ,the generators 2U and 24,

respectively.

The-construction and adjustments of the generatori-24 are suchthat vthesame is .responsive only to the vertical-'control signals of .substan- -tially greater'duration than theVhorizontal-control` signals.

lAs indicated in the drawings, the' tube I II is@ supplied with lthe usual operating potentials.

Y'Circuits -A are-*utilized for the .purpose of defveloping the synchronizing and framing signals `for transmission. These circuits lcomprise an -amplifer' tube-.58 having its-grid circuit connected as lshown to the platecircuit of an amplifier tube 60, and anamplier tube 62 having its grid circuit connected to the plate circuit of an amplifier tube 64. The plates of the tubes 58 andGZ-have a common resistor 66 for the purpose hereinafter explained. The voltage wave appearingacross thev horizontal deecting coils I8 includes a'saw-too'th component and an impulse component, and is applied by a connection 'I2 The relative'amplitudes and shapes of these components and their occurrence Awith respect to the time axis is indicated at 68 and 10, respectively. Hereinafter, the impulse components will be referred to as synchronizing signals.

y'The voltage wave appearing across the Vertical deflecting coils'. 22 also comprisesr a saw-tooth component andan impulse component, and is applied by a connection 'I8 from these coils to the grid of the tube 64. vThe relative amplitudes l.and-shapes of these impulses and their occurrence with respect tothe time axis are indicated at 14. and 16, respectively. Hereinafter, the irnpulse components Will be referred to as framing signals` The synchronizingsignals occur at the required frequency and are .of the proper shape, amplitude and duration for synchronizing purposes.

.. Also, the framing signals occur at the required` frequencyand are of the proper shape and amplitude for framing purposes. The synchronizing signalson the grid circuit of the tube 60 and the framing signals on the grid circuit of the tube -64 are of vpositive polarity for the reason p that the return-line voltages across. the coils I8 and 22 are of positive polarity. This is because f .the most efficient `operationpof the output tubes Myo'nd plate-current cut-oft, and the return-line scanning voltages are of the order of hundreds of volts, while the picture scanning voltages represented by the saw-tooth component are below 10% of the value of the return-line voltages. Also, the picture voltages are negative, while the return-line voltages are positive. For these reasons,` the synchronizing and framing signals on the plates of the tubes 8l] and 64, respectively, are in the form of negative impulses, as indicated at 80 and 82, and are of amplitude corresponding 'to' plate saturation of the respective tubes. Also,

the framing signals, occurring at' the rate of 48 a second, are of greater duration than the synchronizing signals which occur at the rate of 5832 a second, by an amount corresponding to the diierence between the duration of the horizontal control signals and the vertical control signals. Since both tubesv 68 and 64 are biased beyond cut-off so that only the positive returnline voltages are eifective to cause them to draw plate current, and to drive them to plate-current saturation, the signals in their plate circuits are flat-topped.

'- The tube 58 operates to amplify the synchronizing signals, which are of positive polarity in -the plate circuit of this tube, as indicated at 84.

The tube 62 operates to amplify the framing signals, whichv are of positive -polarity in the plate circuit of this tube, as indicated at 86.

The synchronizing and framing signals are mixed in the resistor 65, and are supplied by a connection 88 to an amplifier circuit B.

The synchronizing and framing signals, as amplified in the circuit B, are then'used for three distinct purposes, as follows: (a) by means of a connection 90, these signals are takenV from a suitable stage of the circuit B; whereat the same v are of sufficient amplitude and of negative polarity, as indicated vby the Figure 92, and are applied to the grid 26 for the purpose of cutting oii the ray I6 during the horizontal and vertical return-line periods; (b1) by means of a connection 94, the synchronizing and framing signals are taken from a suitable stage of the circuit B, whereat the same are of suflicient amplitude and of negative polarity, as indicated by the Figure 96, and are applied to a selected stage of the amplifier 40 whereat these signals are effective to block out this amplifier during the horizontal and vertical return-line periods. In this manner, the ampliiier 4U is prevented from passing and amplifying undesirable signals which might be developed during these return periods; and (c) by means of a connection 98, the synchronizing and framing signals are taken from a suitable stage of the circuit B, whereat they are of sufiicient amplitude and of positive polarity, as indicated by the Figure 100, and are applied Vto a stage of the amplifier 40 which is beyond the l stage at which the connection 94 is made, as indicated in the drawings, the action being to cause the synchronizing and :framing signals to be ampliiied and transmitted with the picture signals from this point on. The amplitude of the synchronizing and framing signals in the connection 98 is such that they drive the tube supplied by this connection beyond the point of platecurrent saturation. In this manner, and by making the connections 94 and 98 as explained, the synchronizing and framing signals transmitted with the picture signals are flat-topped and are accompanied by practically no extraneous signals which otherwise might operate at the receiving stations to interfere with proper synchronizing action.

In operation, the amplitude of the framing signals is adjusted until they are substantially equal to the synchronizing signals. This is accomplished by adjusting the potentiometer |82 in the plate circuit of the tube 54. As stated, the synchronizing and framing signals are negative on the grids of the tubes 58 and 82 which are cut 01T by these signals. Any signals of positive polarity are blocked or prevented from passing by these tubes because no negative bias has been provided therefor, as represented in the drawings, and the grids of these tubes are prevented from swinging positive due to grid current in the high resistance shown connected in the grid circuits.

The width of the synchronizing signals is ei?-V changed by adjusting the bias voltages on the first impulse tubes S8 and 64.

While it is contemplated to supply the tubes 88 and 66 directly from the vdeiiecting coils i8 and 22, or from the deiiecting plates: when these are used, it will be understood that the connections 'l2 and 'i8 can be made from other points in the respective generators 2l] and 24 which provide the impulses having the proper amplitudes, durations and time occurrence for, derivation of the f synchronizing and framing signals. In such case,

the connections 'l2 'and I8 shown are omitted, and

theconnections made as indicated by the broken lines 72a andla;

In the system as just described, several of the synchronizing signals would appear simultaneously with each framing signal, as indicated in Figs. 2 and 3. On account of the fact that the fra-ming frequency of 48 cycles is made to be an uneven multiple of the synchronizing frequency of 5832 cycles, in order to obtain the so-calledV interlaced scanning action referred to, the distribution of the synchronizing signals with respect to the framing signal for the odd frames, as represented in Fig. 2, is different than such distribution for the even frames, as represented in Fig. 3. The effect of this in the amplifier B is to produce a resultant framing signal of a somewhat different Wave shape for the odd frames than for the even frames. These framing signals of-different 4shapes have a varying control effect at the receiving apparatus which causes the same to drop out of frame unless all adjustments are exactly right. By my invention, however, occurrence of any synchronizing signals simultaneously with the framing signals is prevented, so that each framing signal has substantially the same shape. When represented graphically, the signals will appear as indicated in' Fig. 2a. which corresponds to Fig. 2, and as indicated in Fig. 3a which corresponds to Fig. 3. The manner in which this desirable action is obtained in my improved system will now be eX- plained.

The framing signals in the output circuit of the tube 64, and which are of, negative polarity,

The Width Of the-T as indicated at 82, are appliedby a connection |68 to the grid circuit of an amplifier tube ||0. These signals drive the tube ||0 to saturation, so that the framing signals appear in the plate circuit as square-topped signals of positive polarity, as indicated at ||2, and which, as shown, are applied to the grid circuit of a second amplier tube ||4. Thesefsignals drive the tube ||4 to saturation, and appear in the plate circuit thereof as square-topped signals of negative polarity, as indicated at ||6. By a connection H8, these negative signals are applied to a suppressor grid |20 with which the tube 58 is provided, and are of sufficient amplitude to drive the suppressor grid far enough negative so that this tube is cut off regardless of occurrence of the synchronizing signals on the grid |22. During the periods of occurrence of the framing signals, therefore, the tube 58 does not amplify or pass any synchronizing signals. The framing signals for both the odd and even frames then appear in the connection 88, amplifier B and connections 90, 94 and 98, as represented in Figs. 2a `and 3a, without distortion by any synchronizing signals. framing signals as received at the receiving stations has substantially the same shape, and each is therefore of equal eiect and influence in keeping the receiving apparatus in frame. Y

With the purpose in mind of transmitting synchronizing signals continuously, even during the periods of occurrence of the framing signalsybut without interference with the latter, I propose to embody my invention in a television transmission system as shown in Fig. 4, in which the parts and connections corresponding to those in Fig. 1 have been designated by the same respective reference characters as the latter.

The operating action in Fig. 4 is just-the opposite of that in Fig. l in the sense that instead of the framing signals being utilized to cut out the synchronizing signals during the framing periods, as in Fig. 1, the synchronizing signals are utilized to cut out the framing signals for the periods during which the two kinds of signals would otherwise occur simultaneously.

In Fig. 4, an additional tube |24 is used to supply the grid circuit of the tube l| l0 Ywith the synchronizing signals of negative polarity, as indicated at |26. The grid circuit of the tube |24 is supplied by a connection |28 with the voltage wave across the horizontal deecting coils |8 and comprising the saw-tooth component and the impulse component, as indicated at 68 and 10,' respectively. The bias on the tube |24 is such that it passes only the impulse components. The bias on the tube |||l is such that the synchronizing signals are eiective to saturate this tube at a relatively low amplitude, so that these signals, appearing in the plate circuit and being then of positive polarity, are of somewhat greater duration than the synchronizing signals appearing in the connection 88. This is indicated at |38. The synchronizing signals of greater duration are applied to the grid circuit of the tube H4, and appear in the plate circuit thereof as negative signals, as indicated at |32. If required, the bias on the tube ||4 may be made such that the synchronizing signals in the plate circuit thereof are of somewhat greater duration than these signals in the grid circuit of this tube.

By a connection |34,'the negative synchronizing signals of greater duration are applied to a suppressor grid |36 with which the tube 62 is provided, and are of suicient amplitude to drive The result is that each of the A the suppressor grid far enough negative so that this tube is cut off regardless of occurrence of the framing signals on the grid |38. During :the periods of occurrence of the. synchronizing'sign nais, therefore, the tube 62 does not amplify or pass the framingv signals. By reason of this action, the framing signals for the odd frames will be interrupted, as represented in'Fig. 5, topravide interruption periods for occurrenceofthe synchronizing signals indicated at 84. Similarly, the framing signals forthe even frames will be interrupted, as represented in Fig; 6, to provide interruption periods for occurrence of Vthe syningY signals-are Vtransmitted continuously, without interruption by the framing signals, and without interfering-with the effectiveness ofthe framing signals at the receiving apparatus.

Considering the broadest aspect of Vthe embodiment of my invention shown in Fig. 4, Ibelieve myself tobe the rst to propose the method of operation in a'television systemwherein signals at a relatively low or framing frequency and synchronizing signals at a relatively high frequency are developed in separate electricalchannels respectively, wherein there are developed, from-the signals at the relatively low frequencyyframing signals each of which is interrupted, and wherein the synchronizing signals and the interrupted framing'signals are supplied to a common am- Vpliiier channel under conditions. such that all signals are of the same polarity, and such that'the periods-of interruption 'of the framing'signals are in phase with the periods of occurrence ofthe synchronizing signals.

Iti will be understood thatthe various values of resistance, capacity, voltage and frequencies have been given by way of example only, and that these can bevaried overa substantial rangeto meet different requirements.

While but one embodiment of my invention has been shown and described, it will be understood that various changes within the conception of those skilled in the art can be made without departing from the spirit of my invention or `the scope of the claims.

I claim as my invention:

1. In a television system wherein it is required that synchronizing signals and framing signals be transmitted in the same electrical channel, a circuit for developing the synchronizing signals, aV circuit vfor developing the framing signals, an electrical channel supplied from said circuits and in which both the synchronizing and framing signals appear, and connecting vr'neansbetween said circuits. for applying to one of said circuits the signals developed in the other circuit and under such conditions that the signals so` applied are effective at the time to suppress operating action of said one of said circuits. Y

2. In the art of television, the method of operation which comprises scanning an object to develop picture signals, developing separatively synchronizing and framing signals to control the scanning action, and utilizing the signals of one kind to suppress. the signals of the other kind.

3. In the art of television, the method of operation which comprises scanning an object to develop picture signals, developing separately synchronizing and framing signals to control the scanning action, and utilizing the framing signals to suppress the synchronizing signals.

4. In the art of television, the method of operation which comprises scanning an object to develop picture signals, developing separately synchronizing and -framing signals, and utilizing the synchronizing signals to suppress at least part of the framing signals. Y

5. In the art of television wherein it is required that synchronizing and framing signals be de-4 veloped for controlling the scanning action and transmitted in the same electrical channel and under conditions whereat there are periods of simultaneous occurrence of the ramingsignals and some of the synchronizing signals, the method of operation which comprises scanning an object to develop picture signals, developing separately synchronizing and framing signals to control the scanning action, supplying both kinds of signals to a common electrical channel, and utilizing the synchronizing signals to suppress the framing signals only during such simultaneous periods of occurrence whereby any control action during these periods is only that due to the synchronizing signals.

6. In a television system wherein it is required that synchronizing signals and framing signals be transmitted in the same electrical channel, a circuit for developing one kind of signals and including an electron tube, a circuit for developing the other kind of signals and including an electronY tube provided with a grid, an electrical channel supplied from said circuits and in which both the synchronizing and framing signals appear, and connecting means between the output circuit of said rst-named tube and said grid for applying to the latter the signalsV in said output oir-' cuit and under such conditions of polarity that each of the signals so applied is effective to cut oir said second-named tube.

7. In a television system wherein it is required that synchronizing signals and framing signals be transmitted in the same electrical channel, a circuit for developing synchronizing signals, a circuit for developing the framing signals and including an electron tube provided with a grid, an electrical channel supplied from said circuits and in which both the synchronizing and framing signals appear, and means for applying to said grid signals occurring in time with the synchronizing signals and each being greater in duration than the latter and each being of such polarity when applied to said grid to cut off said second-named tube.

8. In a television system wherein it is required that synchronizing signals and framing signals be transmitted in the same electrical channel, a circuit for developing the synchronizing signals and including an electron tube provided with a grid, a circuit for developing the framing signals and including an electron tube, an electrical channel supplied from said circuits and in which both the synchronizing and framing signals appear, and means for applying to said grid the signals in the output circuit of said second-named tube and under such conditions of polarity that each of the signals so applied is eiective to cut 01T said iirst-named tube.

9. In a television transmitter, means for generating comparatively narrow electrical synchronizing impulses which occur at a comparatively high frequency, means for generating comparatively wide unslotted electrical framing impulses which occur at a comparatively low frequency, means for producing slots in each of said wide impulses of such width and so located that said narrow impulses may be inserted therein, and means for adding said narrow impulses and said slotted impulses.

l0. In a television transmitter, means for generating substantially rectangular narrow electrical impulses which occur at a comparatively high frequency, meansI for generating substantially rectangular wide electrical impulses which occur at a comparatively low frequency, means for producing gapsl or slots in said wide impulses which are of such width and which occur insuch time relation that said narrow impulses may be inserted therein, and means for adding said narrow impulses and said slotted wide impulses.

il. In a television transmitter for transmitting a composite signal comprising picture signals, comparatively high frequency synchronizing impulses and comparatively low frequency framing impulses, means for producing said synchronizing impulses, means for producing said framing impulses, a plurality of amplier channels, said first means being connected to one of said channels, said second means being connected to another of said channels, means for adding the outputs of said channels, and means for rendering one of said channels ineffective to transfer a signal during the occurrence of one of said impulses which is being supplied to another of said channels.

12. In a television transmitter, means for generating substantially rectangular narrow elec trical impulses which occur at a comparatively high frequency, means for generating substantially rectangular wide electrical impulses which occur at a comparatively low frequency, an amplifier channel connected to said rst means, a second amplifier channel connected to said second means, means for rendering said second channel ineffective to pass a signal for approximately only the period that said narrow impulses and said wide impulses occur simultaneously, and

means for adding the outputs of said amplier channels.

13. In a television transmitter, means for generating substantially rectangular electrical fram- Ving impulses', an amplier channel connected to said means, and means for blocking said channel a plurality of times during the occurrence of one 

